Over the years various analog to digital converter systems have been devised. One of the wider used systems has been the so-called dual slope integration technique that is used somewhat extensively in digital volt-meters and similar systems. In this technique an integrator is allowed to integrate the analog signal in one sense for a period of time. Next a constant current is applied to the integrator to cause it to integrate back down to zero. The time required to return the integrator to zero is a measure of the amplitude of the analog signal, and the counter counting that time interval is a digital representation of the analog signal.
While quite satisfactory for signals of a relatively limited amplitude range, the usefulness of the so-called "dual slope" method greatly decreases in the presence of input signals varying in amplitude over a wide dynamic range. To accommodate such widely varying signals, various users have resorted to programmable gain amplifiers in combination with voltage to frequency converters to achieve the desired accuracy for such wide dynamic ranges. With these systems the output of the amplifier is applied to the voltage to frequency converter and the frequency output counted. The output of the counter is applied to a digital to analog converter, which output analog signal is subtracted from the input signal at the input to the programmable gain amplifier. Even systems of this type are somewhat limited in their ability to accommodate wide dynamic ranges.
Another approach taken to accommodate a wide dynamic range is the use of dual integrators and in these systems, two integrators are used, one or the other being switched OFF as it reaches a predetermined level, while the other is used to continue the integration. While these systems function adequately, they are somewhat expensive and require complex switching to achieve the desired dynamic range.
It is therefore an object of this invention to provide an improved method for converting analog signals having a wide dynamic range to digital form.
Another object of this invention is to provide an improved apparatus for converting analog signals having a wide dynamic range to digital form.